Breath of Fire II/ROM map

The following ROM data was obtained from an old Gamefaqs thread (link) by a user called StarryKnights.

Characters starting information

Initial data for the game's characters. Information block starts at x00:087C ($C0:087C) and ends at x00:0D3B ($C0:0D3B) (Assuming no header). 
Each entry is 64 bytes long.  This data follows the RAM PC data setup from the RAM map, though, much of this start up data goes unused.

Layout:

01-04: Character Name
05: Unused (In-game compared to RAM, setting this value to 20 would make the PC sprite into Valerie)
06: Unused (PC Status)
07: Character's PC Number
    00 - Ryu
    01 - Bow
    02 - Rand
    03 - Katt
    04 - Nina
    05 - Jean
    06 - Sten
    07 - Spar
    08 - Bleu
    09 - Kid Ryu
    0A - Kid Bow (Zombie in battle)

8: Initial level
9-10: Unused (Current health)
11-12: Initial Max HP
13-14: Unused (Current AP)
15-16: Initial Max AP
17: Shaman Form
18: Initial Strength
19: Initial Stamina
20-21: Initial Agility
22: Initial Condition
23-24: Initial Weapon (Value 11 tells the game that you have a weapon equipped)
25-26: Initial Shield (Value 21 tells the game that you have a piece of armor equipped)
27-28: Initial Armor (Value 21 tells the game that you have a piece of armor equipped)
29-30: Initial Helmet(Value 21 tells the game that you have a piece of armor equipped)
31-32: Initial Accessory 1 (Although set to 00 00 on most characters, this is bugged as you're not supposed to be able to unequip 'nothing')
33-34: Initial Accessory 2 (Although set to 00 00 on most characters, this is bugged as you're not supposed to be able to unequip 'nothing')
35-36: Unused (Current Attack)
37-38: Unused (Current Defense)
39-40: Unused (Current Vigor)
41: Unused (Current Wisdom)
42-43: Unused (Current Luck)
44: Initial Guts
45: Initial Wisdom Base
46: Initial Luck Base
47-49: Initial EXP
50-64: Unused

There are three sets of characters in this data block. 
First Set: Normal game, for the most part. 
Second Set: Consists solely of Kid Ryu and Kid Bow. Adult Ryu and Adult Bow inherit their stats from their kid forms. (Worth noting if you want to change their starting stats)
Third Set: What I can only surmise are the team's stats during the title screen demos.

Stat gain tables

Stat Gain Tables:
----
Hex offset (HiROM Address)
x05:71B0 - x05:5DEF ($C5:71B0 - $C5:5DEF)

4 bytes, split into 8 half-bytes in this order with a max increase of '15 (F)' per stat: 

Byte 1: HP, AP
Byte 2: Strength, Stamina
Byte 3: Unused, Agility
Byte 4: Wisdom, Luck

Almost every character seems to have extra level gains for levels they don't join at. These are not used at all due to the initial data. 
Also, it seems Bleu's stats uses the Monster Table as her level up data so she doesn't have her 'own' to modify without some serious stat table moving.

Guts gain upon level is consistently the same for every level up.  Each PC's gain starts at: 
x01:8FE5 ($81:8FE5)

Enemy information

Enemy stats:

59000-5A8FF

Bytes 1-8: Name

9-10: Hit points

11-12: AP

13: Luck

14-15: Attack

16-17: Defense

18-19: Agility

20: Drop rate???

21-22: Experience

23-24: Zenny

25: Item set

26-32: Unknown

For detailed information on how drop rates and item sets work, check out Ben Siron's handbook that explains many of the game's mechanics: link

Spell gains table

Pointers: 5AA00-5AA011

5AA12-5AADE

Pairs of bytes. First is for level the spell is gained on, the second is the spell gained. 00 terminates.